Okay. You say. I like working on my cars and can do most things,
but I just can not solder. Every time I try, I make a bloody mess of it.
Well you are probably right, most people have problems soldering. It is
not magic, just a lack of understanding what you are trying to do. It is
a skill to be learned and practice will make it near perfect. There two
basic principles to soldering.

....No.1 The work pieces to be soldered must be
mechanically and chemically CLEAN.
....No.2 There must be sufficient HEAT applied to successfully complete
the operation.

Clean mechanically means that the joint to be soldered
has been prepared to fit properly, either by placement or filing etc. to
make the pieces fit. Improper fitting components makes it hard to get a
good joint. If it is a previously soldered joint that broke, the old
solder must be removed to refit the joint. It also means that any
corrosion, dirt, grease or rust be removed. The joint must also be
chemically cleaned as well as physically prepped, This means the use of
a flux or acid applied to the joint components. Usually when soldering
brass components a good sanding to bright metal and a mild paste type
flux is all you need. When steel is the material it must be sanded or
filed and then it takes an acid in liquid form to clean or etch the
steel well enough chemically.

The Flux cleans the materials chemically and then allows
the solder when heated properly to flow into and around the joint for
maximum strength, The solder must flow quite freely. Just blobbing it on
will not do. There must be a chemical, mechanical and heat bonding of
the solder and the joint components.

That brings us to the heat part of the job. Get a good
soldering iron. It must provide at least 60 watts so a small tip
electronics soldering iron will never get those larger joints done. I
have for 34 years used a Weller 100/140 watt soldering gun. It has
plenty heat to get the job done. They also make a larger version but I
find it too clumsy to handle. There are also some newer soldering pencil
type irons out there of sufficient wattage that stay hot all the time
and sit in a holder. Which ever type you have, or get, keep the tips
tight and clean before using make sure the tips are tinned well with
flux and solder and wiped off with a rag to make them nice and shiny.
Keep a damp sponge or rag handy to wipe the hot tip off every so often
from the build up of flux and oxidation. If not they will limit the heat
available for a good joint. A good joint will have a smooth shiny look
and solder will have flowed enough to give a filleted look.

The solder used must be a good grade I prefer at least a
60/40 composition. That's sixty percent lead and forty percent tin. The
best solder will have a rosin flux core. Which will do nicely for most
jobs. If you use acid core keep it away from your motors and any wiring
as it will eat them up with corrosion as well as rust any steel parts of
your chassis or what ever. If you must use acid flux on steel components
after soldering rinse the whole job off with hot water, and then dry and
relube any bearings or bare metal areas.

I know the environmental wackos have restricted the sale
of lead based solder and that remains your decision what to use but I
have not found the new lead free solders to be worth a damn as far as
making a good strong joint. You can still search out and find the good
stuff. Many of the large electronic supply houses keep it on hand for
their big companies that need it for good work.

Following these tips will mean you have a much better
chance of doing a good job. Practice will make you much better at it.
Many will tell you that to do it right you must apply the heat to the
joint with the gun and then add the solder to the joint. That is good
practice but not always possible. It is more important to have the joint
held in position so it can not move, this will involve at least one hand
to hold it. I heat my soldering iron up and apply the solder to the tip
in sufficient quantity until it forms a small molten drop, then
carefully apply the tip to the joint and let the solder flow off into
the joint and make sure to keep the heat there till the solder does flow
as it should. If you need more to complete the joint redo the same
procedure and reheat the joint till the new solder flows into the whole
joint and fills any gaps. I hope these ideas will help you out and that
your solder jobs become something you can be proud of.